The present invention relates to voltage translators, and more particularly, to an ECL to TTL translator which eliminates current spikes in the output thereof.
As is well known, many of today's complex systems mix and match integrated circuits (ICs) of different logic families to accomplish a series of interrelated functions. In one example, signals produced in a one logic family, ECL, are translated to levels compatible with another logic family, TTL, for further processing. A typical ECL to TTL translator converts a differential ECL input signal to first and second complementary control voltages for driving upper and lower transistors of an output stage respectively. The collector-emitter conduction paths of the upper and lower transistors are serially coupled between a positive supply voltage, V.sub.CC, and ground potential. The complementary control voltages are generated in independent conduction paths coupled between power supplies, V.sub.CC and V.sub.EE, typically operating at 5 volts and -5.2 volts respectively. The currents flowing therethrough are made large, typically 7 milliamps (ma) or greater, for rapid switching of the control voltages, but not without the cost of considerable power consumption.
During logic transitions, as the differential ECL input signal passes through zero, the upper and lower transistors of the output stage are simultaneously enabled allowing undesirably large currents to flow therebetween. These current spikes induce noise into the power supplies causing a myriad of problems in adjacent circuits including false logic switching. The greater the frequency of operation, the greater the noise problem. Furthermore, the inherent base discharge time of the output stage transistors may permit one transistor to turn on before the other one turns off again enabling simultaneous conduction and current spikes.
Hence, there is a need for an improved ECL to TTL translator which eliminates current spikes in the output signal during logic transitions. The improved ECL to TTL translator should be operative with reduced quiescent currents and consume less power.